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Figure 18-17. Traditional spanning tree design
In a 6500 environment using VSS supervisors, we can create a single logical switch from
two physical switches. This new logical switch is called a VSS cluster (see Chapter 17
for more information). Since the two links from each bottom switch connect to a single
logical switch, STP is not needed. A VSS cluster design is shown in Figure 18-18. The
bottom switches see the VSS cluster as a single endpoint and can make a single port
channel to that device. Cisco describes this as two switches with a single control plane.
Figure 18-18. A 6500 VSS design
This solution is much cleaner, since spanning tree is not required. Each link can now
be fully utilized, doubling the uplink speed from the bottom switches.
Nexus does not support VSS technology and instead uses vPCs. With vPCs, the top
switches are not bonded into a single logical switch, but the bottom switches still see
them as a single endpoint when creating port channels. Figure 18-19 shows two
switches connected to two Nexus 7000s using vPCs for all connections. Cisco describes
the Nexus vPC arrangement as two switches having one data plane and two control
planes.
Let’s walk though the steps needed to configure a vPC.
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